Once the plant bolts (producing a stalk on which flowers will grow) the leaves lose their flavor, so pinch back frequently to keep flowers at bay. Growing plants in partial shade during a hot spell can help prevent bolting. Succession planting every 2-4 weeks will ensure constant cilantro for your kitchen. Let some plants go to seed - you can dry them for use as coriander, save for future plantings, or let drop for yet more cilantro plants!